1. Field of the Invention
The present invention concerns a feeding apparatus for cellulosic material in which a screw feeds and compresses the material between a screw shaft and screw housing for the build-up of a pressure tight material plug.
2. Brief Description of the Related Art
In treatment of cellulosic material, such as refining in a grinding apparatus, steam is formed, which is separated from the material, retaining its high pressure, to be utilized separately in the process. However, discharge of the material separated from the steam is done at a lower pressure, such as atmospheric pressure. In order to prevent the steam from leaving with the material and to maintain the high pressure of the steam, the material must be fed out through sluice means of any kind. Another way to seal the steam separating portion from the discharge of the material is to allow the material at the discharge to form a pulp plug, which seals the outlet so that the steam will not be entrained in the material when discharged.
In known outlet means of the latter type, the material is provided to fall down into a screw, which is, in one end, provided with drive means and in the opposite end feeds the material towards a throttling opening so that the material plug is formed. Since the driving is provided on the pressure side, the drive means must be sealed by means of pack boxes or the like, which wear out and require maintainance and possibly replacing. The plug is also formed in the end of the relatively long screw, which is opposite to the drive means, wherefore the higher load on this end of the screw makes the screw unstable. This also limits the possibilities to control the forming of the plug depending on the loading conditions.